It is known that for example, in a measuring instrument adapted to measure the pH of a sample stored in a container using a glass electrode and a reference electrode, in a measurement state of measuring the pH of the sample or in a calibration state of using a calibration liquid having a known pH to correct the relationship of the potential difference generated between the glass electrode and the reference electrode with a measured value, an internal solution of the reference electrode gradually flows out from a liquid junction part provided in the reference electrode and is thereby reduced, and therefore in order to compensate for the shortage, the internal solution is appropriately refilled from a refilling port.
(Patent Literature 1)
For example, in the case of a measuring instrument adapted to continuously take in a sample using a sampling mechanism or the like to measure the pH of the sample, an internal solution of a reference electrode contacts with the continuously flowing sample through a liquid junction part and diffuses, and thereby the internal solution of the reference electrode is thinned or the internal solution flows out from the liquid junction part. Therefore, it is necessary to continuously or regularly refill the internal solution in a measurement state.
Also, in order to continuously perform the measurement with accuracy, it is necessary to calibrate measured values using a calibration liquid not only at the start of the measurement but at intervals of a predetermined period, and therefore it is necessary to regularly feed the calibration liquid while the sample is being continuously measured.
On the other hand, it has been thought that in a waiting state of performing neither the measurement nor the calibration, it is only necessary to refill the internal solution at the start of next measurement, and therefore a change in the amount of the internal solution has never been cared about from the beginning.
Further, it has been thought that for example, in particular, in a measuring instrument adapted to acquire a tiny amount of sample and continuously measure the pH of the sample, the sample in a waiting state is stopped from flowing, and only a tiny amount of the sample remains in a flow path, and therefore as compared with in a measurement state where the sample constantly flows, in the waiting state, the diffusion of an internal solution is unlikely to occur.
For these reasons, in a conventional measuring instrument of a continuous measurement type, refilling an internal solution in a waiting state has not been considered.
Also, since a calibration liquid has not been used in a waiting state of not performing calibration, refilling the calibration liquid in the waiting state has not been conventionally considered as well.
However, the present inventor has first found that when keeping a measuring instrument of a continuous measurement type as described above in a waiting state for a predetermined time or more, there occurs the problem that a calibration liquid or an internal solution evaporates inside a flow path that is provided for refilling the calibration liquid or the internal solution in a calibration state or a measurement state, and thereby crystals are precipitated from the calibration liquid or the internal solution to clog the flow path.